Russia's second largest city, St. Petersburg, has introduced a law that bans "homosexual propaganda," RIA Novosti reported.

According to the news agency, the law allows authorities to fine individuals up to 5,000 rubles ($170) and companies up to 500,000 rubles ($17,000) for "the promotion of homosexual, lesbian, bisexual, and transgender practices among minors." It claims to seek to protect the "health, moral and spiritual development of the underaged."

It effectively outlaws all public events in support of gay rights, which are prohibited anywhere children might be present. St. Petersburg has previously allowed gay pride marches, unlike Moscow, which was sanctioned by the European Court of Human Rights for repeatedly withholding permission for the events.

The bill was passed by St. Petersburg's legislative assembly at the end of last month and signed into law by Governor Georgy Poltavchenko on Sunday. It is due to come into effect within 10 days.

The city is the fourth – and so far the largest – in Russia to pass such legislation, after Arkhangelsk in the south, and Ryazan and Kostroma in the center.

The Russian Orthodox Church's representative on youth issues, Dimitri Pershin, called today for the legislation to be introduced nationwide.

Meanwhile local and international rights activists have vowed to campaign for its repeal, the Guardian reported, with global gay rights group All Out calling on supporters to avoid travelling to St. Petersburg until the ban is revoked.

Amnesty International condemned the law as "a thinly veiled attempt to legalize discrimination" when it was first proposed in November 2011.

"The notion that [lesbian, gay, bisexual, transgender and intersex] rights activists are somehow converting Russia’s youth through 'propaganda' would be laughable, if the potential effects of this new law weren't so dangerous and wide-reaching," said the campaign group's Europe and Central Asia program director, Nicola Duckworth.

Homosexuality remained a crime in Russia until 1993 and an official mental illness until 1999. Homophobia is still prevalent in Russian society, Miriam Elder wrote in a piece for GlobalPost last year, with bynationalism, conventional gender roles, and the hyper-traditional values of the Russian Orthodox Church all playing a role.